Catalyst compositions comprising metallocene complexes activated by alkylalumoxane activators (or cocatalysts), were introduced to the art of polymerization catalysis in the mid-1970s. Alkylalumoxanes exhibit several inherent problems in use, such as a need for high (alumoxane):(metallocene) ratios to produce highly active catalyst compositions, high reactivity toward impurities (moisture, alcohols, etc.) and flammability. Accordingly, some of the developments in this area of catalysis involved a search for alternative cocatalysts capable of activating metallocene complexes.
The class of alkylalumoxanes comprises oligomeric linear and/or cyclic compounds represented by the formulas R--[Al(R)--O].sub.n -AlR.sub.2 for linear oligomeric alumoxanes and [--Al(R)--O--].sub.n for cyclic oligomeric alumoxanes where R is a C.sub.1 -C.sub.8 alkyl group. If R is the methyl group, the compound is called methylalumoxane or MAO. MAO has been the most widely used cocatalyst in metallocene catalyst systems.